In the laser technology, non-linear optical devices such as second harmonic generator, upper or lower frequency converters, optical parametric oscillator and the like can be produced by use of non-linear optical effect of crystals. The laser obtained directly by using a laser crystal is limited in wave band; furthermore, there is still lack of non-linear optical crystal of excellent performance in the deep ultraviolet band.
At present, the ultraviolet non-linear optical materials include: BBO (β-BBO) crystal, LBO (LiB3O5) crystal, CBO (CsB3O5) crystal, CLBO (CsLiB6O10) crystal and KBBF (KBe2BO3F2) crystal. Crystal growth techniques for these materials have become more mature, but there are still some significant deficiencies, for example, the crystal is deliquescent and has a long growth cycle; although KBBF has a ultraviolet cut-off edge of 155 nm, its layer-by-layer growth habit hinders the further application. Therefore, searching for new non-linear optical materials in deep ultraviolet band is still an important and arduous task.
From the perspective of exploring non-linear optical materials, prerequisites for industrialization and application are stable compound, simple system and stable performances. Based on the strong frequency-doubled effect of β-BBO and short cut-off edge of PbB4O7 and SrB4O7, it is of very important significance to explore new compounds in the Ba—B—O system.
In recently years, in the development of various types of novel non-linear optical crystals, the researchers around the world are still trying to explore new non-linear optical crystals, which have a simple system and are easy to prepare and stable in performance, to find out practical non-linear optical crystals which can convert a laser at a limited wavelength into a laser in a new band by use of frequency-doubled effect, wave-mixing effect, optical parametric oscillation and other non-liner optical effects. Such a technique can fill in the spectrum blank in wavelengths of the lasers emitter by various laser devices and prompt more extensive application of the laser devices.